day etal



Jan. 10, 1956 J. DAY ETAL 2,730,450

CERAMIC DIELECTRIC AND PROCESS OF PREPARING IT Filed June 17, 1953 2 Sheets-Sheet l Jan. 10, J, DAY r CERAMIC DIELECTRIC AND PROCESS OF PREPARING IT Filed June 17, 1953 2 Sheets-Sheet 2 a V Z as f is negative (of the order of 850.l-

United States Patent-O CERAMIC DIELECTRIC AND PROCESS OF PREPARING IT Jean Day and Micheline Calis, Paris, France, assignors to Compagnie Generale dc Telegraphic Sans Fil, a French corporation Application. June 17, 1953,Serial No..362,32 6 Claims priority, application France 'July 1, 1952 i 3 Claims. (Cl. 106-39) The present invention relates. to ceramic dielectrics or low power factor, suitable for electric capacitors of high quality intended for radio-electric apparatus of high he quency.

Ceramic dielectrics intended for such use should present a high dielectric constant with a temperature coefiicient as low as possible, low power factor, high insulation resistance and high dielectric strength.

While compositions which may be baked at relatively low temperatures, for example, below 1350 C., so as to utilize ovens of low cost and high efficiency would be most advantageous, the difficult technological problem arises of reproducing ceramic pieces that are identical from one oven. charge to the next.

The difliculty of this problem is aggravated by a number of factors involved, such for example as the baking temperature, the temperature curve as a function of the. time of baking, the proportions of the components, the origin, the purity and the physico-chemical character of. the components.

Ceramic dielectrics are known which have a low power factor'of about 0.2-per cent at 1 megacycle. The principal'component of such dielectrics is either a silicate of magnesium (steatite), the dielectric constant of which is approximately 6 and the temperature coefficient of which is slightly positive (of the order of l00. 10- or titanium oxide, the dielectric constant of which is approximately 80, and the temperature coefficient of which By suitable. proportions of the components, it is possible to attain any temperature coefficient in the range between that of steatite and that of. titanium oxide, from -+l00.10* to -850.l0- To each value of the temperature coefficient there corresponds avalue of dielectric constant and there" is substantially alinear law between the. two limiting values above mentioned. Moreover a composition is known which has a dielectric constant in the neighborhood'of 200 with a temperature coefficient that is very low, only within narrow temperature limits of about +10 to +50 C. In general that temperature interval is insufiicient to meet the specifications of cap-acitor manufactures.

Ceramic dielectrics with zero or slightly negative temperature coefficient can be reproduced only with difliculty. On the one hand, a slight change in the dielectric formula (which may occur in case of a slight error of weight of one of the components) results in wide variation in temperature coefiicient. On the other hand the baking temperature has a great influence upon the value of the temperature coefficient for compositions of the type wherein a slight change of the composition (we are concerned with the final composition as determined by X-ray analysis which depends at the same time upon the weight of oxides in the paste composition, the baking temperature, the atmosphere in the oven, etc), brings about a wide variation in temperature coefficient. Accordingly, it is very difficult to attain an accurately predetermined temperature coeflicient with such compositions.

2,730,450 Patented Jan. 10, 1956 Grams TiOg 34 to 45 ZrOz 40 to 27 BaCOa 9 to 7 ZnO 4 to 3 $1102 l to 10 Aluminum silicate 12 to 18 The following description and the accompanying drawings given byway of non-limitative example, will assist in understandingv the invention Fig. 1 shows the variation of dielectric constant temperature coefiicient'KO as a function of the dielectric constant e of ceramic materials generally that have low power factor.

Fig. 2 shows the variation of temperature coefficient K 3 as a function of the percentage of a given component x of known compositions (curves a and b) and of acomposition according to the inventiontcurve c), and

Fig. 3 shows the variation of the temperature coefficient K0 as a function of the percentage of the Shoe component of a product according to the invention.

Known ceramics of low power factor afford a dielectric constauh. which, depending on the proportions of components, varies between 6 and approximately 100. The corresponding temperature coethcient K0 is substantially a straight line function of such dielectric constant e, such as shown on Fig. 1. The temperature coefiicient as well as the dielectric constant vary as a. function of the proportion x of some one component of the composition according to curves such as a and b, Fig. 2. It is seen that the variation is very sharp for proportions of x below 10 per cent. Now in the mass production of ceramic pieces, errors of weight in some one component frequently occur. Moreover it is difficult. to assure homogeneity of the paste. Consequently accidental variations in the proportions of components are practically inevitable. Therefore the manufactured pieces are rarely identical, with consequent large proportions of rejects in manufacture.

The composition of the present invention obviates this difficulty by reason of the fact that it affords a variation curve of K0 as a function of x, such as shown at c, Fig. 2. it is seen that this curve is relatively fiat and it is evident that despite the errors in weight, and the lack of homogeneity above pointed out, the product will be approximately uniform.

The range of composition above referred to comprises limits sufiiciently wide to meet extreme conditions. Most satisfactory results are obtained with the following range of proportions:

Grams TiOz 37 to 42 ZrOz 35 to 30 BaCOa 9 to 7 Zn() 4 to 3 SnOz 3 to 8 Clay 11 to- 9 In this formula the optimum proportion of 81102 is in the neighborhood of 5 per cent.

Frequently aluminum silicate is used in the form of a clay. The clay known as ,Provins" gives excellent results.

When the proportion of SnOz is varied in a composition such as above defined, K varies according to a curve such as shown in Fig. 3.

By varying the proportions of the other components between the foregoing limits, K0 likewise varies but little. Consequently a slight error in weight in any component or an accidental lack of homogeneity of the mix would introduce but a very slight variation in K0. Therefore, great dependability of manufacture and great reduction in rejects are attained. 1

The manufacture of the ceramic product in question is efiected by well known procedure. The components are weighed and crushed to fine powder. The components are mixed for example in a ball mill, the bowl and balls of which are of porcelain. -The powdered mix thus obtained is converted into a paste by adding an organic binder. by any known procedure, as for example, by molding or extrusion. The pieces thus obtained are subjected to baking at a temperature between 1200 and 1350 C. If it is desired to regulate the contraction of the pieces, the

mix may be subjected to a preliminary baking operation at a temperature between 1100 and 1300 C. After such preliminary baking, the mass is crushed again and reduced to a fine powder. The powder thus prepared may then be treated according to the procedure previously described. There could, if desired, be added to the prebaked powder, powder of the same composition which had not been prebaked.

The dielectric constant of ceramic according to the invention may be between to 30. The following composition has a temperature coefiicient which varies but slightly from a mean of -25.l0":

Grams TiOi 45 37 SnOa Provins clay 10 The dielectric pieces are formed from the paste The mineral elements of the compositions according to the present invention may easily be determined in practice by diffraction analysis. Manifestly chemical analysis admits of checking the proportions of these elements in the finished product to assure that they are substantially identical to the composition of the paste, bearing in mind the elimination in the course of baking of CO: from the component BaCOa. Consequently the composition of the product may readily be ascertained from that of the paste and conversely.

As many changes could be made in the above composition and many apparently widely different embodiments of this invention could be made without departing from the scope of the claims, it is intended that all matter con tained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent of the United States is:

1. Ceramic dielectric product consisting essentially of:

Grams TiOz 34 to 45 Z102 40 to 27 BaO 7 to 5 ZnO 4 to 3 Smog l to 10 Aluminum silicate clay 12 to 18 2. Ceramic dielectric product consisting essentially of:

Grams TiO: 37 to 42 ZrOg 35 to 30 BaO 7 to 5 ZnO 4 to 3 S: 3 t0 8 Clay 11 to 9 3. Ceramic dielectric product consisting essentially of:

Grams TiOa 45 Z10: 37 BaO 6.4 ZnO 3.6 SnO: 5 Clay 10 References Cited in the file of this patent UNITED STATES PATENTS 2,424,111 Navias July 15, 1947 2,533,140 Rodriguez Dec. 5, 1950 2,668,118 Jonker Feb. 2, 1954 

1. CERAMIC DIELECTRIC PRODUCT CONSISTING ESSENTIALLY OF: 